An intramedullary fixation method for operation on proximal femur fracture is conventionally known, wherein the method uses a nail inserted into a femur diaphysis from a bone head in a vertical downward direction and a lag screw obliquely inserted into a through hole located at an upper side of the nail.
Also, a fixing structure for fixing a nail and a lag screw by utilizing a pressing force generated by screwing a stopper screw, which is a lag screw having a bite-in thread at a front end portion thereof, is conventionally known. In this fixing structure described in Japanese Patent Application No.: JP 2007-236568 A (hereinafter Patent Document 1), a method for fastening a screw and a method for preventing rotation of a screw, which utilize a conventional art in a normal way, are used.
Meanwhile, the above-described intramedullary fixation method directly rotates a lag screw via a guide apparatus for bone surgery to advance the lag screw according to a lead of the lag screw toward a bone head suffering fracture and perform threading, and then holds the lag screw. It is sometimes difficult, however, to create a thread by threading due to a density of a cancellous bone.
Such guide apparatus for bone surgery that executes threading by directly rotating a lag screw is commonly known as a target device. The target apparatus includes an arc-shaped guide apparatus body (frame) coupled to a base portion of a nail by screwing and a guide sleeve fixedly connected to the frame, and the frame includes a connecting portion at which the frame is connected to the base portion of the nail and a guide portion extending substantially in parallel with the nail so as to create a predetermined constant gap between the connecting portion and the guide portion. The guide sleeve is fixedly connected to the guide portion of the frame and is held via the frame in a position confronting a transversal hole provided on the nail, so that various tools and bone surgery equipment such as a bone connection tool are inserted into and guided through the guide sleeve. As an example of this kind of guide apparatus, Japanese Patent Application No.: JP 2011-115408 A (hereinafter Patent Document 2) discloses a guide apparatus for attaching an osteosynthesis device, the apparatus includes a nail introduced into a marrow of a femur and a lag screw inserted into a bone head part of the femur so as to intersect with the nail.
The above-described fixing structure, however, has a problem in that fastening achieved by the structure could become loosened and is thus unstable, because the structure substantially utilizes only a pressing force from an end portion of the lag screw. Another problem is that a bone holding power merely achieved by a holding power of a screw is not sufficient for fixing a bone suffering severe osteoporosis.